Needle bearing and method for grinding bearing parts thereof

ABSTRACT

It is an object of the invention to provide a needle bearing which can prevent occurrence of flake and seizure in the bearing parts even under such severe lubricating condition as provided by a compressor for a car air conditioner or a planetary unit for an automatic transmission. The needle bearing is structured by barrel grinding the raceway surface of a ring and the surface of a rolling body without using a ceramic-related abrasive such as alumina or silicon carbide.

BACKGROUND OF THE INVENTION

The present invention relates to a needle bearing which is used in a carair conditioner or in a planetary unit for an automatic transmission.

In a compressor for a car air conditioner or in a planetary unit for anautomatic transmission, as a bearing for supporting a thrust loadapplied to a rotary part, there is used a thrust needle bearing.However, in the compressor for a car air conditioner, since HFC134a(Hydro Fluoro Carbon 134a) or PAG (Polyalkylene glycol) is used as arefrigerant or operating oil, the lubricating condition of the bearingis under a very severe environment. And, the rotation condition of thebearing also ranges widely from high speeds to low speeds, and furtherthe load to be applied to the bearing ranges from a condition of almostno load to a condition of about 5000 N; and, depending on the operatingconditions of the compressor, these conditions are combined together atrandom.

Therefore, under the environment requiring such severe lubricatingcondition, there is required a thrust needle bearing which can providebetter lubricating performance and, to satisfy such requirement,conventionally, for example, the surface roughness of a ring or arolling body is enhanced or, as shown in FIGS. 19A and 19B, in a thrustring 1, there are formed notches 2 which are used to secure an oilpassage. Also, as shown in FIG. 20, in order to secure the passing oilamount of lubricating oil, the collar portions 4 of an outer ring 3 areturned over to thereby increase the opening height h.

However, in the compressor for a car air conditioner or in the planetaryunit for an automatic transmission (A/T), originally, since thelubricating condition is very severe, the above-mentioned measures canprovide little effect. Also, because the lubricating condition is verysevere, for example, there occurs metal contact between the ring androlling body. Therefore, in case where foreign substances higher inhardness than the rolling body are sticking to the raceway surface ofthe ring and the pocket inner surface of the retainer to be contactedwith the rolling body, the rolling body is worn due to the influence ofthe foreign substances, thereby raising a fear that the bearing can beflaked or seized.

SUMMARY OF THE INVENTION

The present invention aims at eliminating the above-mentioned drawbacksfound in the conventional needle bearing. Accordingly, it is an objectof the invention to provide a needle bearing which can prevent theoccurrence of the flaking and seizure even under such severe lubricatingcondition environment as provided by a compressor for a car airconditioner or a planetary unit for an automatic transmission.

In attaining the above object, according to a first aspect of theinvention, there is provided a needle bearing comprising: a retainerhaving a plurality of pockets; rings; and a plurality of rolling bodiesrollably incorporated in the respective pockets of the retainer androlling on raceway surfaces of the rings, wherein at least one of theretainer, the rolling bodies and the rings is free from a foreignsubstance having hardness equal to or higher than the hardness of thebase material of the rolling bodies.

According to a second aspect of the invention, there is provided amethod for grinding bearing parts, wherein, when grinding surfaces ofthe bearing parts made of metal using abrasives, the abrasives havehardness lower than hardness of base material of the bearing parts, andthe surfaces of the bearing parts are grinded using the abrasives by atleast one of barrel grinding, shot blasting, and shot peening.

Also, according to a third aspect of the invention, there is provided aneedle bearing comprising: a retainer having a plurality of pockets;rings; and a plurality of rolling bodies rollably incorporated in therespective pockets of the retainer and rolling on raceway surfaces ofthe rings, wherein at least one of the retainer, the rolling bodies andthe rings is free from, on the surface thereof, a foreign substancehaving a mean diameter of larger than 30 μm.

In the first to third aspects of the invention, as specific means forpreventing a foreign substance having hardness equal to or higher thanthe hardness of the base material of the rolling bodies or a foreignsubstance having a mean diameter larger than 30 μm from being present onthe surface of the ring, there can be employed a method for barrelworking the raceway surface without using a ceramic-related abrasivesuch as alumina (hardness Hv of 1800 to 2200) or silicon carbide(hardness Hv of 2500 to 3000), that is, a method for barrel working theraceway surface using an abrasive lower in hardness than the basematerial of the rolling bodies and ring of the bearing. And, in the caseof the method using a ceramic-related abrasive, as a post-working step,there is used a barrel polishing method for polishing the needle bearingusing plastic material, wall nut material and corn material (coat ofcorn), or a method for removing the ceramic-related abrasive through awashing operation. By the way, the mean diameter of the foreignsubstance here means the mean of the major minor diameters of oneparticle.

According to a fourth aspect of the invention, there is provided aneedle bearing comprising: a retainer having a plurality of pockets;rings; and a plurality of rolling bodies rollably incorporated in therespective pockets of the retainer and rolling on raceway surfaces ofthe rings, wherein, in case where 0.01 mm² of the surface of at leastone of the bearing parts, that is, the retainer, the rolling bodies andthe ring is set as a unit area, the rate per unit area of existence ofhard foreign substances having hardness equal to or higher than thehardness of the base material of the rolling bodies and sticking to thesurfaces of the bearing parts is set equal to or less than 10%.According to a fifth aspect of the invention, there is provided a needlebearing comprising: a retainer having a plurality of pockets; rings; anda plurality of rolling bodies rollably incorporated in the respectivepockets of the retainer and rolling on raceway surfaces of the rings,wherein, in case where 0.01 mm² of the surface of at least one of thebearing parts, that is, the retainer, the rolling bodies and the ring isset as a unit area, the number per unit area of hard foreign substanceshaving hardness equal to or higher than the hardness of the basematerial of the rolling bodies and sticking to the surfaces of thebearing parts is set equal to or less than 300.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of the structure of a needle bearing accordingto an embodiment of the invention;

FIG. 2 is a graphical representation of the bus shape of the surface ofa rolling body obtained when glass beads are used as abrasives;

FIG. 3 is a graphical representation of the bus shape of the surface ofa rolling body obtained when alumina oxide is used as abrasives;

FIG. 4 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 1, shown in Table 1 before and after a wear test isconducted;

FIG. 5 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 4, shown in Table 1 before and after a wear test isconducted;

FIG. 6 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 5, shown in Table 1 before and after a wear test isconducted;

FIG. 7 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 9, shown in Table 1 before and after a wear test isconducted;

FIG. 8 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 8, shown in Table 1 before and after a wear test isconducted;

FIG. 9 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 11, shown in Table 2 before and after a wear test isconducted;

FIG. 10 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 13, shown in Table 2 before and after a wear test isconducted;

FIG. 11 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 18, shown in Table 2 before and after a wear test isconducted;

FIG. 12 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 22, shown in Table 2 before and after a wear test isconducted;

FIG. 13 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 15, shown in Table 2 before and after a wear test isconducted;

FIG. 14 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 31, shown in Table 3 before and after a wear test isconducted;

FIG. 15 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 32, shown in Table 3 before and after a wear test isconducted;

FIG. 16 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 37, shown in Table 3 before and after a wear test isconducted;

FIG. 17 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 42, shown in Table 3 before and after a wear test isconducted;

FIG. 18 shows the shape of a bus of a rolling body used in a samplebearing, sample No. 39, shown in Table 3 before and after a wear test isconducted;

FIGS. 19A and 19B are a perspective view of a thrust ring used in aconventional thrust needle bearing; and,

FIG. 20 is a section view of the structure of a conventional radialneedle bearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, description will be given below of the preferred embodiments of aneedle bearing according to the invention with reference to theaccompanying drawings.

FIG. 1 is a section view of the structure of a needle bearing accordingto an embodiment of the invention. As shown in FIG. 1, a needle bearingaccording to the present embodiment of the invention comprises a ring11, a plurality of rolling bodies (needle-like rollers) 12, and aretainer 13.

The ring (hardness Hv of 650 to 800) 11, rolling bodies (hardness Hv of700 to 800) 12 and retainer (hardness Hv of 650 to 800) 13 arerespectively made of metal such as SUJ2. In the retainer 13, there areopened up a plurality of pockets (not shown) for holding the rollingbodies 12 in a rollable manner, while the pockets are disposed atregular intervals in the circumferential direction of the ring 11. Also,the rolling bodies 12 as well as the raceway surface 11 a of the ring 11and the pocket inner surfaces 13 a of the retainer 13 to be contactedwith the rolling bodies 12 are worked by barrel grinding using anabrasive (such as a glass bead (hardness Hv of 400 to 500) and a metalball (hardness Hv of 400 to 600)) lower in hardness than the basematerial of bearing parts such as the rolling bodies 12 and ring 11 inorder to remove scales and burrs produced when the present needlebearing is heat treated.

When barrel grinding the bearing parts of the thrust needle bearing, incase where the surfaces of the bearing parts are ground using anabrasive lower in hardness than the base material of the bearing parts,there can be obtained the following effect. That is, even in case wherethe abrasives are not removed perfectly in a washing step after agrinding operation but the abrasives are left on the surfaces of thebearing parts, when the thrust needle bearing is in actual use, theremaining abrasives are bitten into and crushed in, for example, betweenthe thrust ring 11 and rolling bodies 12. Therefore, even in case wherethe abrasives are left on the surfaces of the bearing parts, they existno longer as foreign substances which are higher in hardness than thebase material of the bearing parts, thereby being able to reduce theinfluence of the abrasives remaining on the surfaces of the bearingparts.

To confirm the above effect, the present inventors, using a thrustneedle bearing having an inside diameter of 40 mm, an outside diameterof 60 mm and a thickness of 5 mm (rated dynamic load: 24000 N) as a testbearing, have conducted a rolling body wear resistance test under thefollowing test conditions: that is, the axial load: 2000 N, the radialload: 0 N, the rotation speed: 2000 min⁻¹, lubricating oil: kerosene(PAG=9:1), and test time: 48 hrs. And, after completion of the test, thepresent inventors have observed the rolling body surfaces of therespective test bearings. FIGS. 2 and 3 show the results of ourobservation.

Specifically, FIG. 2 shows the bus shape of the rolling body surfacewhen glass beads (#120, diameter of the order of 0.1 to 0.2 mm) wereused as the abrasives, whereas FIG. 3 shows the bus shape of the rollingbody when aluminum oxide was used as the abrasives.

As can be seen from the observation results shown in FIGS. 2 and 3, whenaluminum oxide was used as the abrasives, in 48 hrs. after start of thetest, the rolling body 12 wore down to a position shown by a solid linein FIG. 3. On the other hand, in case where glass beads were used as theabrasives, when compared with the case using aluminum oxide as theabrasives, the wear of the rolling body 12 was improved greatly.

The above observation results show the following facts. That is, whenbarrel grinding bearing parts made of metal, preferably, the surfaces ofthe bearing parts may be ground using abrasives having lower hardnessthan the base material of the bearing parts. Specifically, because thehardness of the abrasives is lower than that of the base material of thebearing parts, even in case where the abrasives are not removedperfectly in a washing step after a grinding operation but the abrasivesare left on the surfaces of the bearing parts, when the thrust needlebearing is in actual use, the remaining abrasives are bitten into andcrushed in, for example, between the thrust ring 11 and rolling body 12.Therefore, even in case where the abrasives are left on the surfaces ofthe bearing parts, they exist no longer as foreign substances which arehigher in hardness than the base material of the bearing parts, therebybeing able to reduce the influence of the abrasives remaining on thesurfaces of the bearing parts.

By the way, the invention is not limited to the above-mentionedembodiment. For example, in the above embodiment, as the abrasives forgrinding the surfaces of the bearing parts, there are used glass beads;however, as the abrasives, there can also be used a metal ball (diameterof about 1 mm) lower in hardness than the base material of the bearingparts. Also, in the above embodiment, the surfaces of the bearing partsare worked by barrel grinding. However, they may also be worked by shotblasting or by shot peening.

By the way, the inventors observed the bearing as to the wear conditionsgenerated therein and found, in the raceway surface and rolling bodies,not only bitten traces caused by foreign substances such as worn metalpowder but also worn states caused by microscopic foreign substances.When observing these bitten traces and worn states in more detail, ithas been confirmed that the same bitten traces and worn states arerepeatedly left in the raceway surface and rolling bodies of thebearing.

The above observation results suggest that the bearing is worn due tomixture of the foreign substances into the raceway surface and rollingbodies: that is, it is assumed that the foreign substances are fixed tothe raceway surface and rolling body (the foreign substances are buriedinto one of the raceway surface and rolling body which is lower inhardness), the thus buried foreign substances repeatedly damage therolling body to thereby cause the rolling body to wear.

Thus, the present inventors also observed the raceway surface androlling body of the bearing as to their initial states before they areworn due to the foreign substances. According to the results of thisobservation, it has been confirmed that, in the initial states as well,there are repeatedly caused similar bitten traces to the above case.Further, on the raceway surface of the bearing in the initial state, thepresence of the foreign substance was also confirmed and, when theforeign substance was checked for the component thereof, the componentwas found a ceramic component such as aluminum oxide which is anon-metal component.

Further, when the raceway surface of a bearing, which had not been used,was observed, such ceramic-related foreign substance as mentioned above,such as alumina, was found. This shows a possibility that the foreignsubstance has been already stuck to the bearing when assembly of thebearing is completed. It is believed that a media (an abrasive) and acompound used when the bearing is worked by barrel grinding are left onthe raceway surface of the bearing to provide such foreign substance.

The above observations and assumptions show a possibility that a smallamount of media remaining on the raceway surface of the bearing cancause the bearing to wear and thus can shorten the life of the bearinggreatly.

To confirm the above possibility, the present inventors, using a thrustneedle bearing having an inside diameter of 40 mm, an outside diameterof 60 mm and a thickness of 5 mm (rated dynamic load: 24000 N) as a testbearing, have conducted a rolling body wear resistance test under thefollowing test conditions: that is, the axial load: 2000 N, the radialload: 0 N, the rotation speed: 2000 min⁻¹, lubricating oil: kerosene(PAG=9:1), and test time: 48 hrs. And, the number of foreign substancesper unit area existing on the bearing raceway surface and the maximumdiameter of the foreign substances were confirmed through an electronicmicroscope before start of the test; and, after completion of the test,the rolling body wear amounts of the respective test bearings weremeasured. Table 1 shows the results of the measurement. TABLE 1 Maximumdiameter Abrasive used Number of of foreign Bearing wear Sample inbarrel foreign substance Amounts Nos. grinding substances (μm) (μm) 1 Noabrasive 3 5 0 2 No abrasive 5 11 0 3 No abrasive 9 32 0 4 No abrasive 543 10 5 Alumina 7 7 0 6 Alumina 18 26 0 7 Alumina 20 32 1 8 Alumina 1752 10 9 Silicon carbide 14 33 1 10 Silicon carbide 23 53 15

In Table 1, sample numbers 1 to 4 show sample bearings which areassembled using rings on which barrel working (grinding operation) isnot enforced, whereas sample numbers 5 to 8 show sample bearings onwhich alumina is used as a media or as an abrasive when they are workedby barrel grinding. Also, sample numbers 9 and 10 show sample bearingson which silicon carbide is used as an abrasive when they are worked bybarrel grinding. By the way, in Table 1, the maximum diameter of aforeign substance means the greatest one of the means of the majordiameter and minor diameter of one particle.

Also, the present inventors have observed the surfaces of the rollingbodies of the respective sample bearings after completion of the abovetest. FIGS. 4 to 8 show the results of this observation. Here, FIG. 4shows the bus shape of the rolling body in the sample bearing which isdesignated by the sample No. 1, FIG. 5 shows the bus shape of therolling body in the sample bearing designated by the sample No. 4, FIG.6 shows the bus shape of the rolling body in the sample bearingdesignated by the sample No. 5, FIG. 7 shows the bus shape of therolling body in the sample bearing designated by the sample No. 9, andFIG. 8 shows the bus shape of the rolling body in the sample bearingdesignated by the sample No. 8, respectively. Also, in each of thesefigures, a broken line shows the bus shape of the rolling body beforestart of the test, whereas a solid line shows the bus shape of therolling body after completion of the test.

From the bus shapes of the rolling bodies shown in FIGS. 4 to 8, therecan be confirmed the following facts: that is, in the case of the samplebearing No. 1, since no abnormal condition is found in the shape of therolling body, it is confirmed that the sample bearing No. 1 has not beenworn. Also, in the case of the sample bearing No. 4, the shape of thebus of the rolling body of the sample bearing provides such shape asshown by a broken line before the test, whereas it provides such shapeas shown by a solid line after the test; and, therefore, it is confirmedthat the sample No. 4 has been worn. Further, in the case of the samplebearings Nos. 5 and 9, the media was removed from them by a washingtreatment after completion of barrel grinding and thus theceramic-related media having a mean diameter of 30 μm was not found onthe raceway surfaces of these sample bearings; and therefore, it isconfirmed that the rolling bodies have not been worn by foreignsubstances. In addition, in the case of the sample bearing No. 8, it isconfirmed that the rolling body thereof has been worn up to such aposition as shown by a solid line due to the ceramic-related mediaremaining on the raceway surface of the sample bearing.

From the above test, we can reach the following conclusion. That is, incase where a needle bearing is structured such that at least one of thering, rolling body and retainer of the needle bearing does not includeon the surface thereof a foreign substance equal to or higher inhardness than the base material of the needle bearing, or a substancehaving a mean diameter larger 30 μm, the ring and rolling body can beprevented from wearing. Therefore, even under such severe lubricatingconditions as provided by a compressor for a car air conditioner and aplanetary unit for automatic transmission, the bearing parts can beprevented from being flaked or seized.

Next, the present inventors, in order to check the remaining abrasivesfor the influence thereof, conducted a bearing wear test under thefollowing test conditions I employing not only needle bearings which hadbeen worked by barrel grinding using an alumina-related abrasive (media)but also needle bearings worked by barrel grinding using asilicon-carbide-related abrasive. And, before the test, the rate perunit area (which is 0.01 mm² of the ringway surface of a bearing) of theremaining abrasive was measured; and, after the test, the wear amountsof the rolling bodies of the respective needle bearings were measured.Table 2 shows the results of these measurements.

Test Conditions I

-   (1) Sample bearing: Thrust needle bearing having: Inside diameter:    40 mm, outside diameter: 60 mm, Thickness: 5 mm, Rated dynamic load:    24000 N,-   (2) Axial load: 3000 N-   (3) Radial load: 0 N-   (4) Rotation speed: 1800 min⁻¹-   (5) Lubricating oil: Kerosene (PAG=9:1)

(6) Test time: 48 hrs. TABLE 2 Bearing Abrasive Area occupied wearSample used in by foreign Amounts Nos. barrel grinding substance (%)(μm) Judgment FIG. 11 No abrasive 3% or 0 Good 7 less 12 No abrasive 7 2Good — 13 No abrasive 21 7 No good 8 14 No abrasive 13 3 Good — 15Alumina 22 15 No good 11  16 Alumina 5 5 Good — 17 Alumina 7 4 Good — 18Alumina 12 1 Good 9 19 Alumina 9 0 Good — 20 Silicon carbide 13 5 Good —21 Silicon carbide 4 3 Good — 22 Silicon carbide 11 1 Good 10 

In Table 2, sample Nos. 11 to 13 designate thrust needle bearings inwhich, after they were worked by barrel grinding, the raceway surfacesof the bearings were washed and the media was removed therefrom; sampleNos. 15 to 19 designate thrust needle bearings in which, as an abrasivein barrel working, there was used alumina; and, sample Nos. 20 to 22designate thrust needle bearings in which, as an abrasive in barrelworking, there was used silicon carbide.

As can be clearly understood from the measurement results shown in Table2, the thrust needle bearings designated by the sample Nos. 11, 12, 14,16 to 22 are smaller in the bearing wear amount than the thrust needlebearings designated by the sample Nos. 13 and 15. The reason for this isbelieved that, in the case of the thrust needle bearings, sample Nos. 13and 15, the rate per unit area of the remaining abrasive exceeds 10%,whereas in the case of the thrust needle bearings, sample Nos. 11, 12,14, 16 to 22, the rate per unit area of the remaining abrasive is equalto or less than 10%.

Also, the inventors observed the rolling body bus shapes of therespective bearings after completion of the above test. FIGS. 9 to 13show the results of this observation. Here, FIG. 9 shows the rollingbody bus shape of the bearing, sample No. 11; FIG. 10 shows the rollingbody bus shape of the bearing, sample No. 13; FIG. 11 shows the rollingbody bus shape of the bearing, sample No. 18; FIG. 12 shows the rollingbody bus shape of the bearing, sample No. 22; FIG. 13 shows the rollingbody bus shape of the bearing, sample No. 15, respectively. Also, ineach of these figures, a broken line shows the bus shape of the rollingbody before the test was started, whereas a solid line shows the busshape of the rolling body before the test was ended.

As can also be clearly seen from the rolling body bus shapes shown inFIGS. 9 to 13, in the case of the needle bearings, sample Nos. 11, 18,22, no abnormal condition is found in the bus shapes of the rollingbodies thereof and thus it is confirmed that the rolling bodies havebeen little worn. On the other hand, in the case of the needle bearings,sample Nos. 13 and 15, an abnormal condition is found in the bus shapesof the rolling bodies thereof and thus it is confirmed that the rollingbodies have been worn.

From the above test results, the inventors can reach the followingconclusion. That is, when 0.01 mm² of the raceway surface is used as aunit area, in case where the rate per unit area of a hard foreignsubstance such as the remaining abrasive is set equal to or less than10%, the amount of wear of the bearing parts due to the foreignsubstance such as the remaining abrasive can be reduced, which makes itpossible to prevent occurrence of flaking and seizure in the bearingparts.

Next, the inventors, in order to check the remaining abrasive for theinfluence thereof, conducted a bearing wear test under the followingtest conditions II using not only needle bearings which had beenrespectively worked by barrel grinding with an alumina-related abrasive(media) but also needle bearings respectively worked by barrel grindingwith a silicon-carbide-related abrasive. And, before the test, thenumber per unit area (which is 0.01 mm² of the raceway surface of abearing) of the remaining abrasive was measured; and, after the test,the wear amounts of the rolling bodies of the respective needle bearingswere measured. Table 3 shows the results of these measurements.

Test Conditions II

-   (1) Sample bearing: Thrust needle bearing having: Inside diameter:    40 mm, Outside diameter: 60 mm, Thickness: 5 mm, Rated dynamic load:    24000 N,-   (2) Axial load: 2000 N-   (3) Radial load: 0 N-   (4) Rotation speed: 2000 min⁻¹-   (5) Lubricating oil: Kerosene (PAG=9:1)

(6) Test time: 48 hrs. TABLE 3 Abrasive Number of Bearing wear Sampleused in foreign Amounts Nos. barrel grinding substances (μm) JudgmentFIG. 31 No abrasive 3 0 Good 12 32 No abrasive 280 2 Good 13 33 Noabrasive 340 6 No good — 34 No abrasive 320 3 Good — 35 No abrasive 3003 Good — 36 Alumina 320 2 Good — 37 Alumina 285 3 Good 14 38 Alumina 1351 Good — 39 Alumina 390 10 No good 16 40 Alumina 320 7 No good — 41Silicon carbide 250 4 Good — 42 Silicon carbide 280 4 Good 15 43 Siliconcarbide 330 5 Good —

In Table 3, sample Nos. 31 to 35 designate thrust needle bearings inwhich, after they were worked by barrel grinding, the raceway surfacesof the bearings were washed and the media was removed therefrom; sampleNos. 36 to 40 designate thrust needle bearings in which, as an abrasivein barrel working, there was used alumina; and, sample Nos. 41 to 43designate thrust needle bearings in which, as an abrasive in barrelworking, there was used silicon carbide.

As can be clearly seen from the measurement results shown in Table 3,the thrust needle bearings respectively designated by the sample Nos.31, 32, 34 to 38, and 41 to 43 are smaller in the bearing wear amountthan the thrust needle bearings respectively designated by the sampleNos. 33, 39, and 40. The reason for this is believed that, in the caseof the thrust needle bearings, sample Nos. 33, 39, and 40, the numberper unit area of the remaining abrasives exceeds 300, whereas in thecase of the thrust needle bearings, sample Nos. 31, 32, 34 to 38, and 41to 43, the number per unit area of the remaining abrasives is equal toor less than 300.

Also, the inventors observed the rolling body bus shapes of therespective bearings after completion of the above test. FIGS. 14 to 18show the results of this observation. Here, FIG. 14 shows the rollingbody bus shape of the bearing, sample No. 31; FIG. 15 shows the rollingbody bus shape of the bearing, sample No. 32; FIG. 16 shows the rollingbody bus shape of the bearing, sample No. 37; FIG. 17 shows the rollingbody bus shape of the bearing, sample No. 42; and, FIG. 18 shows therolling body bus shape of the bearing, sample No. 39, respectively.Also, in each of these figures, a broken line shows the bus shape of therolling body before the test was started, whereas a solid line shows thebus shape of the rolling body before the test was ended.

As can also be clearly seen from the rolling body bus shapes shown inFIGS. 14 to 18, in the case of the needle bearings, sample Nos. 31, 32,37 and 42, no abnormal condition is found in the bus shapes of therolling bodies thereof and thus it is confirmed that the rolling bodieshave been little worn. On the other hand, in the case of the needlebearing, sample No. 39, an abnormal condition is found in the bus shapeof the rolling body thereof and thus it is confirmed that the rollingbody has been worn.

From the above test results, the inventors can reach the followingconclusion. That is, when 0.01 mm² of the raceway surface is used as aunit area, in case where the number per unit area of hard foreignsubstances such as the remaining abrasives is set equal to or less than300, the amount of wear of the bearing parts due to the foreignsubstances such as the remaining abrasives can be reduced, which makesit possible to prevent occurrence of flaking and seizure in the bearingparts.

By the way, the invention is not limited to the above illustratedembodiments. For example, in the above illustrated embodiments, theinvention is applied to a thrust needle bearing but, of course, theinvention can also be applied to a radial needle bearing. In the case ofthe radial needle bearing, there can also be employed specifications inwhich a cage and rollers (a retainer and rolling bodies) are employed,and the rolling bodies thereof are all composed of rollers.

As has been described heretofore, according to the first to thirdaspects of the invention, since foreign substances higher in hardnessthan the base material of rolling bodies exist no longer on the surfaceof the ring, the surface of the rolling body and the inner surface ofthe retainer, even under such severe lubricating conditions as providedby a compressor for a car air conditioner and a planetary unit forautomatic transmission, the bearing parts can be prevented from beingflaked or seized.

And, according to the fourth and fifth aspects of the invention, becausethe wear amounts of the bearing parts due to the foreign substances suchas the remaining abrasives can be reduced, the bearing parts can beprevented from being flaked or seized.

1. A needle bearing comprising: a retainer having a plurality ofpockets; rings; and a plurality of rolling bodies rollably incorporatedin the respective pockets of the retainer and rolling on racewaysurfaces of the rings, wherein at least one of the retainer, the rollingbodies and the rings is free from a foreign substance having hardnessequal to or higher than the hardness of the base material of the rollingbodies.
 2. (canceled)
 3. A needle bearing comprising: a retainer havinga plurality of pockets; rings; and a plurality of rolling bodiesrollably incorporated in the respective pockets of the retainer androlling on raceway surfaces of the rings, wherein at least one of theretainer, the rolling bodies and the rings is free from, on the surfacethereof, a foreign substance having a mean diameter of larger than 30μm.
 4. A needle bearing comprising: a retainer having a plurality ofpockets; rings; and a plurality of rolling bodies rollably incorporatedin the respective pockets of the retainer and rolling on racewaysurfaces of the rings, wherein, in case where 0.01 mm² of the surface ofat least one of the bearing parts, that is, the retainer, the rollingbodies and the ring is set as a unit area, the rate per unit area ofexistence of hard foreign substances having hardness equal to or higherthan the hardness of the base material of the rolling bodies andsticking to the surfaces of the bearing parts is set equal to or lessthan 10%.
 5. A needle bearing comprising: a retainer having a pluralityof pockets; rings; and a plurality of rolling bodies rollablyincorporated in the respective pockets of the retainer and rolling onraceway surfaces of the rings, wherein, in case where 0.01 mm² of thesurface of at least one of the bearing parts, that is, the retainer, therolling bodies and the ring is set as a unit area, the number per unitarea of hard foreign substances having hardness equal to or higher thanthe hardness of the base material of the rolling bodies and sticking tothe surfaces of the bearing parts is set equal to or less than 300.